1. Field of the Invention
The present invention relates to an ink set suitable for ink jet recording, and an ink jet recording method, a recording unit, an ink cartridge and an ink jet recording apparatus each using the ink set.
2. Description of the Related Art
An ink jet recording method for color recording conventionally uses aqueous inks comprising dyes having various color tones dissolved in water-soluble media. Three color inks of cyan, magenta and yellow are generally used as color inks.
These color inks are required to have reliability in use for ink jet recording, the ability to provide a sufficient image density, a good drying property, and the ability to form a recorded image with neither blur nor flow when in contact with water or alcohol, and good weather resistance. Particularly, a high-quality ink jet image equivalent to a silver salt photograph has been recently realized, thereby creating demand not only for good image quality but also for long-term storage stability of a recorded image.
A factor that greatly contributes to the storage stability of an image is fading due to exposure to light (hereinafter, called xe2x80x9cfadingxe2x80x9d). Therefore, formation of an image having excellent light resistance is required. Under light, a dye in an image produced with an ink tends to deteriorate, and eventually fading becomes conspicuous. Therefore, a color ink which comprises a dye having excellent light resistance, or a recording medium which can prevent light fading is used to improve the light resistance of an image.
If there is a big difference between the degree of fading in at least two color portions comprising an entire image, however, the color balance of the image tends to be upset when the entire image is exposed to light, and the entire image whose color balance is upset may give the impression that the quality is worsened. For example, in a multi-color image formed with cyan, magenta and yellow color inks, if the cyan has lower light resistance than the other two colors, the portions of the image formed with the cyan ink are greatly faded, thus decreasing the blueness of the entire image after light fading, as compared with the image immediately after printing.
Japanese Patent Laid-Open No. 10-329403 discloses an ink set having cyan, magenta and yellow inks, and the respective images"" xcex94E, the images being produced with the three color inks, are less than 25, 30 and 15 in a one-year pseudo-fading test with office light. However, the residual ratio of reflection density of each color is not discussed, and the respective xcex94E""s of the images formed with the color inks are large. Therefore, the ink set is not said to produce an image having good light resistance. Furthermore, the color balance of a full-color image using the three colors is not disclosed, and long-term storage stability is not expected.
Accordingly, the present invention provides an ink set comprising color inks that produce images having substantially the same xcex94E and good residual ratios of reflection density, thereby maintaining the color balance of an image after long-term storage, and good image quality.
As a result of intensive research on various inks, the inventors found that by using an ink set comprising inks that produce respective images having substantially the same light fading xcex94E and good residual ratios of reflection density, deterioration in image quality after long-term storage can be prevented without losing the color balance of the image. This resulted in the achievement of the present invention.
According to one aspect of the present invention, there is provided an ink set comprising at least three types of inks each containing a colorant and an aqueous medium, wherein in a fading test under conditions that cause fading corresponding to pseudo-indoor sunlight fading through a window for 3 years or more, respective images produced with the respective inks have the same xcex94E or have differences in xcex94E that are 10 or less in a CIELAB color space display system, and each of the respective images has a residual ratio of reflection density of 70% or more.
According to another aspect of the present invention, there is provided an ink set comprising at least two types of inks each containing a colorant and an aqueous medium, wherein in a fading test under conditions that cause fading corresponding to pseudo-indoor sunlight fading through a window for 3 years or more, respective images produced with the respective inks have the same xcex94E or have a difference in xcex94E that is 10 or less in a CIELAB color space display system, and each of the respective images has a residual ratio of reflection density of 80% or more.
By using the ink set having the above construction, it is possible to provide an ink jet recording apparatus, components associated therewith, and various recording methods such as an ink jet recording method, for obtaining a recorded image that maintains good image quality while keeping a color balance after long-term storage.
According to a further aspect of the present invention, there is provided an ink jet recording method comprising a step of discharging inks through orifices according to a recording signal to record an image on a recording medium, wherein the inks constitute the ink set used for ink jet recording.
According to a still further aspect of the present invention, there is provided a recording unit comprising an ink container containing the respective inks constituting the ink set used for ink jet recording, and a head section for discharging the respective inks.
According to a still further aspect of the present invention, there is provided an ink cartridge comprising an ink container containing the respective inks constituting the ink set.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus comprising a recording unit comprising an ink container containing the respective inks constituting the ink set used for ink jet recording, and a head section for discharging the respective inks.
According to a still further aspect of the present invention, there is provided an ink jet recording apparatus comprising a recording head for discharging inks and an ink cartridge provided with ink containers containing inks constituting the ink set for ink jet recording.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.